Vehicles often include a fuel system configured to provide desired amounts of fuel to combustion chambers or cylinders of a vehicle engine at precise times. In one example, such fuel systems include a fuel injector configured to inject fuel into an intake manifold coupled to the cylinder in a manner known as port fuel injection. Additionally or alternatively, the fuel system may include a fuel injector configured to inject fuel directly into the cylinder in a manner known as direct fuel injection. Injecting fuel via direct injection requires injecting fuel at a higher pressure as compared to port fuel injection in order to meet the timing demands of fuel combustion. For this reason, a high pressure fuel pump is often included with a direct injection system in order to pressurize fuel in a direct injection fuel rail supplying fuel to the direct injector.
After a vehicle has been assembled at an assembly plant, each vehicle subsystem may be tested. This ensures that each subsystem is functioning properly after the vehicle has left the assembly plant, such as when the vehicle is delivered to a customer. The first key-on event of a vehicle engine, which may occur after vehicle assembly and before the departure of the vehicle from the manufacturing plant and/or before the sale of the vehicle, may be associated with an engine green start condition. In some examples, an engine green start condition may span a number of key-on events of the engine while the vehicle is still at the assembly plant, during which time a number of functions of the vehicle are tested to ensure vehicle quality. For example, a fuel system may be tested in conjunction with the engine to ensure that fuel is being injected properly into the combustion cylinders (e.g., testing whether injection timing, injection mass, etc. are occurring as predicted/desired). Still other vehicle subsystem tests may require a running engine for completion.
However, during a first key-on event after the assembly of a vehicle, fuel system components may be filled with at least some air. As a result, during an engine green start condition, a fuel pressure at a direct fuel injector may not be high enough to accurately inject a commanded fuel mass. In addition to causing fuel metering errors, until the direct injection fuel rail pressure is adequately high, the injected fuel may not adequately mix with air in the combustion cylinder, resulting in increased soot emissions. Furthermore, for both of these reasons, the engine may stall or not start at all if operating via direct injection during an engine green start condition. Therefore it is desirable not to operate a vehicle with direct injection until the direct injection fuel rail has been adequately primed, that is until the rail has been supplied with fuel at or above a threshold pressure and has been purged of air.
Attempts to prime a fuel system during green start conditions include retarding spark timing until the engine is primed. One example approach is shown by Oertel et al. in U.S. 2008/0314349. Therein, in response to a detected green start condition, an ignition sequence is activated and spark timing is retarded from a normal spark timing (e.g., adjusted to be later than a default spark timing). In this way, air is purged from the direct injection fuel rail via the direct injectors and the ignition of residual fuel in the direct injection fuel rail is rendered insufficient to start the engine. As a result, the engine is not started until the direct injection fuel rail has been sufficiently purged of air and fuel has been introduced thereto.
However, the inventors herein have recognized potential issues with such systems. As one example, combusting fuel at imprecise air-fuel ratios and directly injecting fuel at lower pressures may result in increased soot emissions. Additionally, in fuel systems including both port fuel injection and direct injection, time spent priming the direct injection fuel rail may increase the initial test time, thereby increasing the amount of time the vehicle has to spend at the plant.
In one example, the issues described above may be addressed by a method for controlling fuel injection to an engine, comprising, in response to an engine green start event, injecting fuel to the engine via a port injector while priming a direct injection fuel rail. In this way, engine green starts may be improved.
As one example, in a vehicle configured with an engine having dual fuel injection capabilities, responsive to a first key-on event occurring after the vehicle has been assembled but before the vehicle has left the planet (that is, during an engine green start condition), port fuel injectors may be activated while direct fuel injectors may be deactivated. A high pressure pump configured to pressurize each of the port injection fuel rail and the direct injection fuel rail may be operated to maintain or increase the fuel pressure in each fuel rail. The engine may then be fueled via only the port fuel injectors until a pressure within the direct injection fuel rail is sufficiently high (e.g., has exceeded a threshold pressure). The direct injectors may be intermittently enabled to allow air in the fuel rail to be purged into the combustion chamber. Once the direct injection fuel rail pressure is high enough to ensure accurate direct fuel metering, the direct injectors may be reactivated and the engine may be fueled via both port and direct fuel injection at an injection ratio determined based on engine operating conditions, such as engine temperature.
The technical effect of fueling a green engine via port injection during the priming of a direct injection fuel rail is that fueling errors may be reduced without increasing exhaust emissions. In addition, by priming the direct injection fuel rail while simultaneously running the engine via port fuel injection, the duration of a green start testing procedure may be reduced, thereby reducing the amount of time a vehicle has to be held at a plant after production.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.